The present invention relates to a magnetic recording medium used in an apparatus such as a magnetic disk apparatus; a process and an apparatus for producing the magnetic recording medium; and a magnetic recording and reproducing apparatus incorporating the magnetic recording medium.
Conventionally, a metallic substrate formed from, for example, an aluminum alloy is widely used as a substrate for producing a magnetic recording medium. Usually, such a metallic substrate undergoes texturing, and is used for producing a magnetic recording medium.
Texturing is a process for forming irregularities on a substrate along a predetermined direction (usually in a circumferential direction) of the substrate. When the surface of a substrate undergoes texturing, the crystal orientation of an undercoat film and a magnetic film, which are formed on the substrate, is enhanced, and the magnetic film exhibits magnetic anisotropy, and thus magnetic characteristics, such as thermal stability and resolution, of a magnetic recording medium can be enhanced.
In recent years, instead of a metallic substrate formed from aluminum or similar metal, a non-metallic substrate formed from material such as glass or ceramic has been widely used as a substrate for producing a magnetic recording medium. Such a non-metallic substrate has an advantage that head slap does not easily occur in the substrate, because of the high hardness of the substrate. Furthermore, from the viewpoint of glide height characteristics, such a non-metallic substrate is advantageously used, because of its excellent surface smoothness.
However, a non-metallic substrate such as a glass substrate encounters difficulty in undergoing satisfactory texturing.
In order to solve such problems, there has been proposed formation of a hard film which can be easily textured on a non-metallic substrate formed from material such as glass or ceramic.
For example, Japanese Patent Application Laid-Open (kokai) No. 5-197941 discloses a magnetic recording medium including a non-metallic substrate coated through sputtering with NiP film serving as a hard film which is easily textured.
A magnetic recording medium including a hard film formed on a non-metallic substrate is produced through the following process: the hard film is formed on the substrate in a film formation apparatus such as a sputtering apparatus; the substrate is temporarily removed from the apparatus and subjected to texturing by use of a texturing apparatus; the resultant substrate is again placed in the apparatus; and then an undercoat film and a magnetic film are formed on the substrate.
However, imparting satisfactory surface smoothness to the hard film of the aforementioned conventional magnetic recording medium is difficult. Consequently, the medium exhibits poor magnetic anisotropy and unsatisfactory magnetic characteristics. In addition, the production process for the magnetic recording medium includes complicated production steps, resulting in high production costs. Therefore, there has been keen demand for a magnetic recording medium which can be easily produced.
Japanese Patent Application Laid-Open (kokai) No. 5-143988 discloses a production process for a magnetic recording medium in which magnetic anisotropy is imparted to a magnetic film. The production process disclosed in this publication includes forming an undercoat layer and a magnetic recording layer through sputtering, such that particles of a sputtering target are deposited onto the layers at an incident angle of 30-65xc2x0.
However, in a magnetic recording medium produced through the aforementioned process, the predominant orientation plane of a non-magnetic undercoat film is a (110) plane, and the predominant orientation plane of a magnetic film is a (101) plane. Therefore, the magnetic recording medium tends to exhibits poor magnetic anisotropy, resulting in unsatisfactory magnetic characteristics.
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium which exhibits excellent magnetic characteristics and can be easily produced; a process and an apparatus for easily producing the magnetic recording medium; and a magnetic recording and reproducing apparatus incorporating the magnetic recording medium exhibiting excellent magnetic characteristics.
The present invention provides a magnetic recording medium comprising a non-metallic substrate; a non-magnetic undercoat film; and an orientation-determining film formed between the substrate and the undercoat film, which film determines the crystal orientation of a film provided directly thereon, characterized in that the orientation-determining film has a crystal structure in which columnar fine crystal grains are inclined in a radial direction, and the ratio of a coercive force in a circumferential direction of the medium (Hcc) to a coercive force in a radial direction of the medium (Hcr); i.e., Hcc/Hcr, is more than 1.
A magnetic film has an hcp structure and the orientation plane of the magnetic film is a (110) plane; and the non-magnetic undercoat film has a bcc structure and the orientation plane of the undercoat film is a (200) plane.
The orientation-determining film causes the texture of the following bcc undercoat film to be (200) (hereinafter xe2x80x9corientation-determining filmxe2x80x9d).
The orientation-determining film may comprise one or more elements selected from among Cr, V, Nb, Mo, W, and Ta.
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may comprise an alloy predominantly containing Cr.
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may predominantly comprise CoTa (Ta content: 30-75 at %) or CoNb (Nb content: 30-75 at %), and may have an Fd3m structure or an amorphous structure.
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may predominantly comprise CrTa (Ta content: 15-75 at %) or CrNb (Nb content: 15-75 at %).
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may predominantly comprise NiTa (Ta content: 30-75 at %) or NiNb (Nb content: 30-75 at %), and may have an Fd3m structure or an amorphous structure.
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may comprise a non-magnetic metal having an Fd3m structure.
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may comprise a non-magnetic metal having a C15 structure.
An orientation-enhancing film may be formed between the non-metallic substrate and the orientation-determining film which causes the texture of the following bcc undercoat film to be (200).
Preferably, the orientation-enhancing film comprises a material having a B2 structure or an amorphous structure.
The orientation-enhancing film may predominantly comprise any alloy selected from among NiAl, FeAl, CoAl, CoZr, CoCrZr, and CoCrC.
The orientation-determining film which causes the texture of the following bcc undercoat film to be (200) may comprise an amorphous NiP alloy, and the ratio of a coercive force in a circumferential direction of the medium (Hcc) to a coercive force in a radial direction of the medium (Hcr); i.e., Hcc/Hcr, is more than 1.
In this specification, xe2x80x9cpredominantlyxe2x80x9d means xe2x80x9cin excess of 50 at %xe2x80x9d.
The present invention also provides a process for producing the aforementioned magnetic recording medium, which process comprises forming the orientation-determining film by releasing from a release source film formation particles containing a material constituting the film, and then depositing the particles onto a deposition surface, characterized in that the direction of the trajectory of the film formation particles is determined such that a projection line of the trajectory of the particles formed on the deposition surface lies along a radial direction of the non-metallic substrate, and the incident angle of the trajectory of the particles is 10-75xc2x0 with respect to the non-metallic substrate.
The orientation-determining film may be subjected to oxidation or nitridation.
The orientation-determining film may be formed through sputtering by use of a sputtering target serving as a release source of film formation particles.
When the orientation-determining film is formed, the film may be subjected to oxidation or nitridation by use of a sputtering gas containing oxygen or nitrogen.
The oxidation or nitridation may be carried out by bringing the orientation-determining film into contact with an oxygen-containing gas or a nitrogen-containing gas.
The present invention also provides an apparatus for producing the aforementioned magnetic recording medium, which apparatus comprises a release source for releasing film formation particles containing a material constituting the orientation-determining film, the film being formed through deposition of the particles onto a deposition surface; and means for determining the direction of the trajectory of the film formation particles released from the release source, characterized in that the direction-determining means can determine the direction of the trajectory of the particles such that a projection line of the trajectory of the particles formed on the deposition surface lies along a radial direction of the non-metallic substrate, and that the incident angle of the trajectory of the particles is 10-75xc2x0 with respect to the non-metallic substrate.
The present invention also provides a magnetic recording and reproducing apparatus comprising the aforementioned magnetic recording medium, and a magnetic head for recording data onto the medium and reproducing the data therefrom.